Ordnance QF 18-pounder field gun Mk I.

The Ordnance QF 18-pounder field gun Mk I was the British Army’s standard field gun of the First World War, and after some teething troubles developed into a reliable weapon.

The 18-pounder was developed in the aftermath of the Boer War, where the British Army’s existing artillery had proved inferior to the more modern guns owned by the Boers. The Equipment Committee of 1901 came up with a series of specifications for new guns, and recommended a 13-pounder for the cavalry and an 18-pounder for the field artillery. The two weapons were more similar in size that their designations would lead one to believe - the 13-pounder was a 3in gun and the 18-pounder a 3.2in gun- but the 18-pounder had a much longer barrel.

The final design was a combination of elements suggested by the Woolwich Arsenal, Armstrong’s Elswick Works and Vickers, and the first completed gun was issued as early as 1904.

The original 18-pounder used a wire-wound barrel, and a single action breech. It had a pole trail carriage, which limited the elevation of the gun and thus its maximum range. It had a small shield. The recoil system used a recoil system with recuperator springs mounted in a housing above the barrel. Most of the ammunition produced before the First World War was shrapnel. An experimental HE shell performed well in 1914, and most later production was of that type.

The only major change before the outbreak of the First World War was to make the barrel liner replaceable.

The 18-pounder went to war with the BEF. It soon became clear that each gun was going to fire many more shells than had originally been expected, and under the increased stress of battle the recoil springs proved to be rather fragile. Once they broke the gun was out of action until the springs had been replaced, a slow and complex process. As a result a new entirely hydro-pneumatic recoil system was developed. This was small enough to fit inside the existing housing. The new system made the gun much more reliable. The new recoil system changed the designation of the carriage, with converted carriages becoming the Carriage Mk. I* and carriages built from scratch with the new system the Carriage Mk. II.

The 18-pounder was used by the British, various Commonwealth Armies and the Indian army, and was also produced in India. It remained in service throughout the First World War, where it was the main field gun used by the British army, and into the inter-war period. It was produced in large numbers. Before the outbreak of war 1,126 had been built in Britain and 99 in India. During the war 8,393 were built in Britain and 851 in the United States. The Americans also produced a modified version of the gun, the Gun, 75mm, M1917 (British), for their own use, modified to fire standard French 75mm shells. An impressive 113 million rounds of 18-pounder ammo was produced during the First World War, with over 99 million rounds being fired on the Western Front.

The Mk.II was very similar to the Mk.I, but used a different method of construction for the barrel.

The Mk I was followed by the greatly improved Ordnance QF 18-pounder field gun Mk.IV, which had a new trail, modified recoil system and breech, and was a significant advance on the Mk I, but the new gun didn’t enter large scale production until 1918.

The 18-pounder was also the basis of an anti-aircraft gun, the 13-pounder 9cwt Mk.I, which used relined barrels, 13-pounder projectiles and 18-pounder cases.